A multi-directional key switch is very popular currently, and it is applied widely in cars, mobile phones, notebook computers, music players and other household appliances. The multi-directional key switch generally presents a cursor on a screen, and it has functions similar to a mouse or track ball used in a computer.
U.S. Pat. No. 7,348,512 discloses a multi-directional key switch adopted in a mobile phone, which has a plurality of dome switches disposed beneath the key cap. When a user presses the key cap along some direction of the key cap, the dome switch closest to the pressing point may be turned on, the circuit of the circuit board generates a signal, and then the system appropriately responds pursuant to the signal.
Reference is made to FIG. 11, which discloses a thin input device in the U.S. Patent Application Publication No. 2008/0048649. The thin input device includes an assembly of a housing A, a key cap (manipulation element) B, a magnetic element C, an elastic element D and a displacement detection means F. The total assembly can be directly fixed on or detached from a circuit board G of the mobile terminal. The key cap B can move along any direction. The magnetic element C is disposed inside the key cap B. The displacement detection means F can be electrically connected to an external electrical device. A plurality of Hall sensors are configured in the displacement detection means F, for detecting the movement of the key cap B. The housing A can be directly fixed on or detached from the circuit board G and detachably covers the key cap B. The elastic element D is disposed on the circuit board beneath the key cap B. On the other hand, the elastic element D is substantially fixed on the circuit board G through the housing A. The elastic element D is made of a soft material with excellent elasticity. When the key cap B moves, the elastic element D is deformed to generate a restoring force to pull the key cap B back to the original position.
In U.S. Patent Application Publication No. 2008/0048649, the key cap B moves towards some direction, the magnetic element C immediately moves along with the key cap B. Once the magnetic element C moves, the magnetic field will change in the peripheral space of the magnetic element C. The displacement detection means F can detect this magnetic changes, and then such information is transmitted to the circuit of the circuit board G, resulting that the mobile terminal system can appropriately respond pursuant to the displacement of the key cap B.
Since the elastic element D is formed by a soft material with excellent elasticity, and the weight of the elastic element D, the key cap B and the magnetic element C continuously puts on the elastic element D, so that such weight applies a preexisted downward pressure on the dome switch G1 of the circuit board G. Thus, the dome switch G1 of the circuit board G is easily and accidentally turned on, resulting in a wrong signal sending to the circuit board G. Accordingly, the design proposed by U.S. Patent Application Publication No. 2008/0048649 does not meet industrial demand.